Javascript Event Emitter Object

A simple event emitter object that you can plug into your javascript libraries.

API is very similar to the node.js events.

Install

npm install event-emitter-object

Import

This package exports multiple builds. Developer has the responsibility to choose the one that best fits to her/his needs.

1. Minified (default)

This is basically the source code itself but minified. There are no compilation and polyfills inside. Use it if you already have a compiler (like babel) and polyfills in your project. (which is mostly is the case.)

const EventEmitter = require('event-emitter-object')

2. Polyfilled and minified

The source code compiled with babel (with the configuration that can be found inside babel.config.js file) and minified. This build contains also polyfills which increases the size of the package dramatically. Polyfills added by the configuration that can be found inside the .browserlistrc file.

// just 1498 bytes
const EventEmitter = require('event-emitter-object/dist/polyfilled')

3. Bundle for browsers

The source code bundled with browserify to generate a UMD bundle. This bundle can be imported by html script tag. No compilation and polyfills.

<script src="https://unpkg.com/event-emitter-object@0/dist/browser.js" crossorigin type="text/javascript"></script>

4. Polyfilled bundle for browsers

The source code compiled with babel and bundled with browserify to generate a UMD bundle. This bundle can be imported by html script tag.

<script src="https://unpkg.com/event-emitter-object@0/dist/browser.polyfilled.js" crossorigin type="text/javascript"></script>

Use

Let's say you have a state manager object to control the state of your app.

function StateManager() {}
StateManager.prototype.updateState = function updateState(payload) {
  // update state
  // ...
  // and inform listeners that the state has just updated
  this.emit('update')
}
module.exports = StateManager

To plug event emitter into your state manager:

StateManager.prototype = Object.assign({}, StateManager.prototype, EventEmitter.prototype)

Now, you can listen and emit events within your state manager:

const state = new StateManager()
state.on('update', function() {
  console.log('State updated!')
})

API

on(eventName, callback, opts)

Registers a new listener for a certain event.

emitter.on('someEvent', function() {
  console.log('Some event happened in some emitter.')
}, {
  once: true // default is false
})

once(eventName, callback)

This is a shortcut for the on method with {once: true}:

// instead of doin this:
emitter.on('someEvent', function(){}, {once: true})
// you can do this:
emitter.once('someEvent', function(){})

emit(eventName, args)

Emits a certain event with arguments.

emitter.emit('someEvent')

// or with arguments
emitter.on('anotherEvent', function(arg1, arg2) {
  console.log('Another event emitted with arguments: ', arg1, arg2)
})
emitter.emit('anotherEvent', ['hello', 'world'])

removeListeners(eventName)

Removes all listeners that belong to a certain event.

emitter.removeListeners('someEvent')

flush()

Removes all events and listeners.

emitter.flush()

Babel Polyfills Report

This module uses the following polyfills in its polyfilled builds.

1. es.array.splice
2. es.date.to-string
3. es.object.to-string
4. es.regexp.to-string